In general, an air intake apparatus including an air intake apparatus main body that includes a plurality of pieces bonded to each other along a split plane is known. Such an air intake apparatus is disclosed in Japanese Patent No. 3964690, for example.
Japanese Patent No. 3964690 discloses a manifold (air intake apparatus) for a four-cylinder engine in which blow-by gas (external gas) is introduced into air intake pipes (air intake port). In this manifold disclosed in Patent Document 1, a manifold main body (air intake apparatus main body) including four air intake pipes is configured by bonding a first member and a second member (a plurality of pieces) each having a half structure to each other by vibration welding. In addition to forming the manifold main body, a distribution passage that introduces the blow-by gas into the air intake pipes is formed. The distribution passage for introducing the blow-by gas projects outward from the outer wall surface of the manifold main body. A blow-by gas tube that extends from a cylinder head of the engine is connected to a connector (external gas receiving port) of the distribution passage.